Gulf of Maine Seasonal Sea Surface Temperature Update

Seasonal Patterns in Sea Surface Temperatures

Author

Adam Kemberling

Published

January 8, 2024

About the Updates:

Over the past decade, scientists at the Gulf of Maine Research Institute have led a body of research that highlights the rapid pace of warming in the Gulf of Maine. To keep you informed, we share seasonal updates about conditions in the Gulf of Maine.

Note About the Data: The figures in this report are created using remotely-sensed satellite data as part of publicly funded research efforts. Satellite SST data was obtained from NOAA’s National Center for Environmental Information (NCEI), with all maps and figures displaying NOAA’s Optimum Interpolation Sea Surface Temperature Data.

The Gulf of Maine Region

For analyses like these, it is important to be clear about the spatial extent that “defines” the Gulf of Maine (Figure 1), as different borders could produce different results. The spatial domain we use as the “Gulf of Maine” is displayed below. This area is consistent with previous seasonal and annual reports that scientists at GMRI have produced.

An overhead view of the Gulf of Maine region. Landmasses and political boundaries for the United States and Canada are displayed. A blue dotted line outlining a box with a transparent blue fill is shown to demark where satellite data for the analysis has been used.

Figure 1: Spatial domain used for Gulf of Maine SST analyses. Depth contours are colored at 100 m intervals up to 600 m; deeper blues indicate deeper water depths

Fall Highlights

For this seasonal report we present an analysis of SST for fall (September 1, 2023 - November 30, 2023). During this season, the average SST for the Gulf of Maine was 57.25°F, making it the 14th hottest fall on record for the period of 1982-2023 — the period over which the satellite data used are available. This seasonal average temperature is 0.72°F above the 1991–2020 climatological reference period (CRP) fall average of 56.53°F.

Weekly Temperatures

Table 1 highlights how the SST for each week this fall compares to the 1991-2020 CRP for the area shown in Figure 1. The observed SST, long-term average SST, and SST anomalies (i.e., departures from the long-term average SST) are shown.

fall average SST was on average 0.72°F or more above normal during the fall, with weekly averaged SST anomalies ranging from -1.79°F to +3.85°F.

Table 1:

Average weekly sea surface temperatures in the Gulf of Maine

Table 1. Weekly Average Sea Surface Temperatures - Fall
(September 1, 2023 - November 30, 2023)
One-Week Period Observed Temperature Climatological Average Temperature Anomaly

Sep 01 - Sep 02

63.3°F (17.4°C)

62.7°F (17.0°C)

0.7°F (0.4°C)

Sep 03 - Sep 09

64.4°F (18.0°C)

62.3°F (16.8°C)

2.2°F (1.2°C)

Sep 10 - Sep 16

64.7°F (18.2°C)

61.6°F (16.4°C)

3.1°F (1.7°C)

Sep 17 - Sep 23

59.3°F (15.2°C)

60.8°F (16.0°C)

-1.4°F (-0.8°C)

Sep 24 - Sep 30

58.3°F (14.6°C)

59.8°F (15.4°C)

-1.5°F (-0.8°C)

Oct 01 - Oct 07

58.5°F (14.7°C)

58.7°F (14.8°C)

-0.2°F (-0.1°C)

Oct 08 - Oct 14

57.9°F (14.4°C)

57.6°F (14.2°C)

0.3°F (0.2°C)

Oct 15 - Oct 21

57.6°F (14.2°C)

56.3°F (13.5°C)

1.3°F (0.7°C)

Oct 22 - Oct 28

57.4°F (14.1°C)

55.1°F (12.8°C)

2.3°F (1.3°C)

Oct 29 - Nov 04

55.8°F (13.2°C)

53.9°F (12.2°C)

1.9°F (1.0°C)

Nov 05 - Nov 11

53.6°F (12.0°C)

52.8°F (11.6°C)

0.8°F (0.4°C)

Nov 12 - Nov 18

51.7°F (10.9°C)

51.8°F (11.0°C)

-0.1°F (-0.0°C)

Nov 19 - Nov 25

51.0°F (10.5°C)

50.8°F (10.4°C)

0.2°F (0.1°C)

Nov 26 - Nov 30

50.2°F (10.1°C)

49.9°F (9.9°C)

0.3°F (0.1°C)

Data Source: NOAA OISSTv2 Daily Sea Surface Temperature Data.
Climatological Reference Period: 1991-2020.

Monthly Statistics

Table 2 shows monthly average SST for fall 2023; each month was within 1°F or more above the 1991-2020 CRP. October showed the largest deviation from the long-term climatological average, with an average SST anomaly of 1.08 °F, making it the 12th warmest October on record. September and November were cooler at 0.6 & 0.5°F above the long-term average—coming in as the 14th and 16th warmest September and November on record, respectively.

Table 2:

Average monthly sea surface temperatures in the Gulf of Maine

Table 2. Monthly Average Sea Surface Temperatures - Fall
(September 1, 2023 - November 30, 2023)
Month Rank (1982-2023) Observed Temperature Climatological Average Temperature Anomaly

September

14

61.8°F (16.6°C)

61.2°F (16.2°C)

0.6°F (0.3°C)

October

12

57.7°F (14.3°C)

56.7°F (13.7°C)

1.1°F (0.6°C)

November

16

52.2°F (11.2°C)

51.7°F (11.0°C)

0.5°F (0.3°C)

Data Source: NOAA OISSTv2 Daily Sea Surface Temperature Data.
Climatological Reference Period: 1991-2020.

How Does this Fall Compare to the Past?

2023 is the 14th warmest fall season observed in the Gulf of Maine during the 41 years we have satellite data to analyze, a departure fall seasons in recent years, which experienced well-above average SSTs.

Figure 2: A ranking of the 10 warmest summer seasons for the Gulf of Maine in the satellite record (1982-2023). 2023 was the eighth warmest summer on record.

Marine Heatwave Conditions

The most commonly used definition of a “marine heatwave” (MHW) is when daily average SSTs exceeded the 90th percentile of a climatological (i.e., 30-year) average for at least 5 consecutive days. Gaps of 2 days or less in this threshold do not constitute a break in the MHW event.

Using this broadly accepted definition, the Gulf of Maine has experienced MHW conditions for 7% of this fall. September was the only month this fall where SST was above the threshold of a MHW, ultimately exhibiting these anomalously warm conditions for a total of six days. SSTs for the remainder of the season remained closer to the long-term average, even dipping below that climatological average for almost three weeks from late September into early October.

Figure 4: A timeseries of marine heatwave (MHW) conditions in the Gulf of Maine extending from January 1, 2023 through August 31, 2023. Black lines represent the long-term (i.e., 1991 – 2020) average SST, the 10th percentile, and 90th percentile for a given day in the Gulf of Maine; a solid line (red for marine heatwave or blue for a non-event) indicate the observed SST this year; red (above 90th percentile) and blue (below 90th percentile) shading illustrates how far the observed SST falls from the MHW threshold.

Presenting SST conditions in terms of anomalies ( Figure 5 ) as opposed to absolute values ( Figure 4 ) illustrates in greater detail the magnitude of MHW conditions throughout the fall. The most extreme daily SST anomalies for fall 2023 occurred towards the start of September, with temperatures building to over 3°F above the climatological average above the climatological average before rapidly dropping to cooler for the remainder of the fall. This rapid drop in SST coincided with Hurricane Lee’s passage through the area, demonstrating how atmospheric conditions can alter ocean surface conditions.

Figure 5: A timeseries of daily average SST anomalies in the Gulf of Maine (solid colored line) compared to the long-term climatological mean, 10th, and 90th percentiles (solid black lines) in the Gulf of Maine for the period January 1, 2023 through August 31, 2023. Red portions denote when temperatures have exceeded the 90th percentile, the threshold beyond which conditions can start to be categorized as a MHW

Heatmap of Temperature Anomalies and Heatwave Events

Looking at the full record of daily SST anomalies in the Gulf of Maine (Figure 6), the distinct thermal regime shift beginning around 2010 is evident. Indeed, since 2012, the Gulf of Maine has experienced far more persistent MHW conditions (indicated by solid black lines) than at any other point in the satellite record.

SST anomalies in the Gulf of Maine this fall were lower than in any season since mid-2019. Fall SST in the previous 3 years had been noteworthy for their extended MHW conditions, part of the long-term trend of unseasonably warm fall since 2012 (Figure 2). The relatively mild fall in the Gulf of Maine this year is a contrast to the 2023 spring and summer seasons—which were the 2nd & 8th warmest on record—and stands in stark contrast to fall SST conditions in the broader North Atlantic region (see Figure 10).

Figure 6: Heat map of daily SST anomalies from the beginning of 1982 through spring 2023. Not only do more large warm anomalies (darker reds) appear more frequently in recent years, but the frequency, duration, and intensity of marine heatwave events (black lines) in the Gulf of Maine has become more pronounced in the past decade.

Spatial Distribution of Seasonal Anomalies

From an aerial perspective, the Gulf of Maine experienced mild above-average SSTs during fall of 2023. In general, conditions were relatively mild, exhibiting seasonally-averaged SST anomalies that did not deviate beyond +/- 3°F from the long-term average. There was an east-to-west gradient in seasonally averaged SST anomalies within the Gulf of Maine, potentially representing the influence of the anomalously cool surface water (depicted by the deep blues in Figure 7) entering the study region through the Northeast Channel. The highest seasonally averaged SST anomaly in the Gulf of Maine was 3.05°F - located near Penobscot Bay.

Figure 7: Map of average SST anomalies for each grid cell in the satellite record for spring 2023. The box outlined by the black dashed line denotes the region of study for the analysis (see Figure 1). Darker red regions indicate warmer anomalies.

Monthly Temperature Anomalies

Average monthly SST anomalies are shown in Figure 8. During the month of September, the Gulf of Maine experienced above-average SSTs with the warmest anomalies concentrated along the shallower coastal areas to the west. Colder than average temperatures were present near the Northeast Channel to the east, where the waters are deeper. In October the pattern persisted, but with fewer below-average temperatures in the Northeast Channel area. By November the limited warming of October had reversed, with cooler anomalies again present near the Northeast Channel as well as to the north towards the Bay of Fundy. Across all months a large area of colder than average SST anomalies was present to the southeast of the Gulf of Maine. This area of colder water exhibited the coldest SST anomalies during October. The cold patch appeared to move westward over the course of the fall season, along the edge of the continental shelf.

Figure 8: This series of maps shows the average monthly SST anomaly for September 2023, Ovtober 2023, and November 2023. The box outlined by the black dashed line denotes the region of study for the analysis. Darker red regions indicate warmer anomalies.

Data Sources:

NOAA_ERSST_V5 data provided by the NOAA/OAR/ESRL PSL, Boulder, Colorado, USA, from their Web site at https://psl.noaa.gov/data/gridded/data.noaa.ersst.v5.html.

NOAA High Resolution SST data provided by the NOAA/OAR/ESRL PSL, Boulder, Colorado, USA, from their Web site at https://psl.noaa.gov/data/gridded/data.noaa.oisst.v2.highres.html.

Citing This Work

If you would like to cite this report, please use:

Gulf of Maine Research Institute. 2022. Gulf of Maine Warming Update: Fall 2023

 

A work by Adam A. Kemberling

Akemberling@gmri.org